1. Field of the Invention
The present invention relates to a field winding type generator-motor which is mounted mainly on a vehicle, and operates as a motor upon starting of an engine and also as a generator after the starting of the engine.
2. Description of the Related Art
In general, a generator-motor for vehicle is installed in an engine room. Therefore, the operating temperature of the generator-motor for vehicle becomes extremely high. In addition, the inner temperature of the generator-motor for vehicle becomes further higher due to heat generated when the generator-motor for vehicle operates as a generator or a motor. Therefore, when temperature of the generator-motor for vehicle rises excessively because of continuous operation for long hours or other reason, the generator-motor for vehicle may be out of order because of a breakdown of an internal component or other reason.
Therefore, conventionally, there has been proposed a generator-motor for vehicle, in which, in order to prevent a failure in the generator-motor for vehicle due to a temperature rise, the temperature of the generator-motor for vehicle is measured, and when the measured temperature exceeds a predetermined temperature, field current is restricted to suppress production of electricity so that a thermal load is reduced (see, for example, Japanese Patent Application Laid-Open No. 08-9567).
The conventional technique, however, has the following problems.
In the conventional technique, field current is restricted based on temperature information of the generator-motor for vehicle, which requires a temperature sensor for sensing the temperature to be provided. Therefore, there arises a problem in that cost increase and structure modification of the generator-motor for vehicle may be caused by mounting the temperature sensor.
In addition, in the conventional technique, when the temperature sensor cannot be mounted on the generator-motor for vehicle, the field current cannot be restricted based on a temperature rise of the generator-motor for vehicle. Therefore, there is a problem that production of electricity from the generator for vehicle cannot be controlled, and that a failure in the generator-motor for vehicle due to the temperature rise cannot be prevented.